An Illinois dad who wrote to his estranged wife that “if I can’t have them, neither can you” before the tragic loss of their three young children has pleaded guilty in the case — though he insists he was suffering from mental illness.

Jason Karels, 36, of Round Lake Beach, will be sentenced to life in prison without the possibility of parole, Lake County State’s Attorney Eric Rinehart said Friday after the defendant pleaded guilty but mentally ill to three counts of first-degree charges related to the children’s passing.

Karels admitted responsibility for the tragic passing of 5-year-old Bryant Karels, 3-year-old Cassidy Karels and 2-year-old Gideon Karels during an incident in a bathtub on June 13.

Their mother, Debra, discovered the children at Karels’ home at 200 E. Camden Lane in the Chicago suburb, where police said he left a note reading, “If I can’t have them, neither can you.”

“This case has devastated the Round Lake Beach community and beyond,” Rinehart said in a statement. “We hope that today’s resolution provides some measure of closure, and we will continue to provide support to the family.”

Several members of the family attended the court hearing on Friday.

Karels was arrested after leading police on a pursuit that ended in a crash near an Interstate 80 bridge in Joliet, police said. He was briefly hospitalized following the incident.

After the crash, he told police he was responsible for what happened to his children in the bathtub and that he had attempted to harm himself before leaving the home, where officers later found evidence of the attempt, authorities said.

The parents shared custody of the children but were living separately at the time of the incident, officials said.

A relative has claimed that Jason struggles with mental health issues but had refused to seek psychiatric help, and Debra had reportedly been in the process of filing for divorce after previously experiencing serious problems in the relationship.

However, the mother still hoped to maintain a connection with Jason for the sake of their children and allowed them to spend time with him.